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Posted: 6/30/2013 11:14:03 AM EDT
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Need a little help determining this problem. I have a new build that I did with an 80% lower and an upper kit I put together. The lower works flawlessly with two different rguns 16" uppers I bought. The problem seems to be with the upper I put together from parts purchased from SARCO INC.
When fired I would be able to fire two rounds and then the spent case would stack on top of the partially fed round from the magazine. Sometimes the spent case will be partially in the chamber. upon clearing the jam I noticed that sometimes there will be a dent on top of the new round, where the case starts to taper down to the neck of the new round being fed from the magazine. When loading one round into the mag and firing, the bolt will lock to the rear every time. When cycling spent brass the extractor picks up the case and the ejector will fling it about 5 feet. The upper is a 16" m4 style upper, one of the differences I noticed was no insert for the extractor spring. The extractor spring is fully seated in the extractor, it is a three ring silver spring. I took the front sight block off and measured the gas port in the barrel, it was .073. The gas port lines up with the gas port in the front sight and I get free flow of air from the gas tube into the barrel. The buffer and spring is the standard carbine spring and buffer. I am wondering if I have a problem with the size of the gas port, the lack of the insert for the extractor spring, a buffer spring and buffer too light or just a problem that might go away when everything wears in. Everything was clean and lubricated before firing. The ammunition used was Independence XM193i 556 x 45 FMJ and Hornady .223 55 grain Z-MAX, I had the same problem with both rounds. One other thing I noticed was with the Rguns uppers, there is a much more defined extractor mark on the rim of the case, the sarco upper has a very light extractor mark. Any ideas? I really appreciate any help. |
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